This principle in exercise science refers to the necessity of applying a greater-than-normal stress or demand to the body’s systems during physical activity. For the body to adapt and improve, whether in terms of muscular strength, endurance, or size, it must be challenged beyond its current accustomed capabilities. This controlled increase in demand stimulates physiological adaptations, such as muscle growth (hypertrophy), increased strength, and enhanced cardiovascular efficiency. Without this progressive increase in workload, the body will simply maintain its current fitness level, leading to a plateau in progress. This principle is fundamental to achieving sustained improvements in various forms of training, including progressive overload in strength and endurance programmes.